In order to deal with many forums related to a fourth generation mobile communication and a new technology, 3GPP for establishing a technology standard of a third generation mobile communication system has started to conduct a study on LTE/SAE (Long Term Evolution/System Architecture Evolution) technology by the end of 2004 in a bid to optimize and enhance performance of 3GPP technologies.
The SAE proceeded centering on 3GPP SA WG2 is a study on a network technology having a purpose of determining a network structure in a manner of juggling an LTE job of 3GPP TSG RAN and the purpose of supporting mobility between heterogeneous networks. Currently, the SAE is one of important standardization issues of 3GPP. This is a job to develop a 3GPP system to a system supporting various radio access technologies based on an IP. The job has been progressed to achieve a target of an optimized packet-based system minimizing a transmission delay with a more enhanced data transmission capability.
An SAE upper level reference model defined by the 3GPP SA WG2 includes a non-roaming case and roaming cases of various scenarios. Detail contents may refer to 3GPP standard document TS 23.400a and TS 23.400b. A diagram of a network structure in FIG. 1 corresponds to a simple reconstruction of the SAE upper level reference model.
FIG. 1 is a diagram of a structure of an evolved mobile communication network.
One of main characteristics of the network structure in FIG. 1 corresponds that the structure is based on a 2 Tier Model, i.e., an eNode B of Evolved UTRAN and a Gateway of a Core Network. Although it is not perfectly matched to each other, it is able to say that the eNode B 20 includes the function of a Node B and an RNC of a legacy UMTS system and the Gateway includes a function of SGSN/GGSN of a legacy system.
Another main characteristic of the network structure is that a Control Plane and a User Plane between an Access network and the Core Network are exchanged by an interface different from each other. In the legacy UMTS system, there exist one interface, i.e., Iu, between RNC and SGSN. On the other hand, since an MME (Mobility Management Entity) in charge of processing a control signal has a structure separated from the GW (Gateway), two types of interface, i.e., S1-MME and S1-U, can be used, respectively. The GW can be classified into a serving gateway (hereinafter abbreviated S-GW) 52 and a packet data network gateway (hereinafter abbreviated PDN-GW or P-GW) 53.
FIG. 2 is a diagram of a relationship between an (e)Node B and a Home (e)Node B.
An attempt to increase cell capacity in order to support such a high-capacity service as multimedia content, streaming, and the like and a bidirectional service in the third generation or the fourth generation mobile communication system continues.
In particular, since various transmission techniques of high-capacity are required according to a development of a communication and dissemination of a multimedia technology, it is able to allocate more frequency resources to increase radio capacity. Yet, since the frequency resource is limited, there exist a limit for allocating the limited frequency resource to a plurality of users.
In order to increase the cell capacity, an approach of using a high frequency band and the approach of reducing a cell radius have been tried. If such a cell of a small radius as a pico cell and the like are applied, since it is able to use a frequency band higher than the frequency band used in a legacy cellular system, more information can be delivered. Yet, since more base stations are necessary to be installed in an identical area, cost may dramatically increase instead.
As mentioned in the foregoing description, recently, a femto base station such as the Home (e)Node B is proposed among the approaches of increasing the cell capacity by using a small cell.
A study on the Home (e)Node B 30 has been started to conduct centering on RAN WG3 of 3GPP Home (e)Node B. Recently, the Home (e)Node B is also studied in SA WG in earnest.
The (e)Node B 20 depicted in FIG. 2 corresponds to a macro base station and the Home (e)Node B 30 may correspond to the femto base station. It is intended that the present specification is explained based on a terminology of 3GPP and the (e)Node B is used when a Node B and an eNode B are mentioned together. And, the Home (e)Node B is used when a Home Node B and a Home eNode B are mentioned together.
Interfaces depicted with dotted lines are used for transmitting a control signal between the (e)Node B 20, the Home (e)Node B 30 and the MME 510. And, the interfaces depicted with lines are used for transmitting a data of the user plane.
FIG. 3 indicates a problem according to a prior technology.
As depicted in FIG. 3, if a traffic is overloaded or congested in the interface between the (e)Node B 20 and the S-GW 52 or if the traffic is overloaded or congested in the interface between the Home (e)Node B and the S-GW 52, a downlink data to the UE 10 or an uplink data from the UE 10 is not correctly transmitted and failed.
Or, if the interface between the S-GW 52 and the PDN-GW 53 or the interface between the PDN-GW 53 and an IP (internet protocol) service network of a mobile communication service provider is overloaded or congested, the downlink data to the UE 10 or the upload data from the UE 10 is not properly transmitted and failed.
And, when the UE performs a handover from a cell where the UE is currently receiving a service to a different cell, if the different cell is in a state of being overloaded, a service of the UE is dropped.
In order to solve the aforementioned problem, mobile communication service providers have changed the S-GW 52 and the PDN-GW 53 with a gateway of a high capacity and have built additional equipments, by which entails significantly high cost. And, since the quantity of transceived data geometrically increases, although additional equipment is newly built, it becomes overloaded soon.
Meanwhile, various methods to optimize the S-GW 52 and the PDN-GW 53 without building an additional mobile communication network have been proposed. For instance, a specific IP traffic (e.g., internet service) of the UE is transmitted in a manner of selecting an optimal path in a macro access network and the specific IP traffic is transmitted in a femto access network (e.g., Home (e)NB) in a manner of detouring in a path via nodes of a public network, i.e., a wired network without transceiving the traffic via the path of the mobile communication network. The technique making a traffic detour (Selected IP traffic offload), i.e., a SIPTO has been proposed.
FIG. 4 is a diagram of a concept of a SIPTO (Selected IP traffic offload).
Referring to FIG. 4, such a mobile communication system as an EPS (evolved packet system) is depicted as an example. The EPS system includes an (e)Node B 20, an MME 51, an S-GW 52, and a P-GW 53. And, a Home (e)Node B 30 is depicted as well.
In this case, as depicted in FIG. 4, the SIPTO (Selected IP traffic offload) technique diverts a specific IP traffic (e.g., internet service) of the UE 10 to the nodes of a wired network 70 without passing through the nodes of an IP service network 60 of a mobile communication service provider.
For instance, if the UE 10 is allowed to access the (e)Node B 20, the UE 10 generates a session, which is passing through such a wired network 70 as a public communication network, via the (e)Node B 20 and can perform an IP network service via the session. In this case, service provider policy and subscription information may be considered.
In order to generate the session, in case of the UMTS, a local gateway in charge of a part of function of GGSN or, in case the EPS, a local gateway in charge of a part of function of P-GW (PDN gateway) can be used as a gateway installed near the (e)Node B 20.
This kind of local gateway is called a local GGSN or a local P-GW. A function of the local GGSN or the local P-GW is similar to that of the GGSN or the P-GW.
As mentioned in the foregoing description, the SIPTO technique has proposed a concept of generating a session to divert (offload) the data of the UE to such a wired network as a public communication network via the (e)Node B, i.e., a macro base station.
Yet, since the aforementioned legacy SIPTO technique makes a data of a user pass through a macro base station, i.e., (e)Node B 20, if the (e)Node B 20 is in a state of being overloaded, there still exist a problem.